Federal Treasurer Joe Hockey has flagged possible changes to the eligibility age and indexation of the age pension as measures to help improve the budget bottom line.

The retirement age is already set to climb from 65 to 67 and Mr Hockey has pointed to the United Kingdom, where it will be lifted to 70 in future decades.

He has also discussed the option of indexing the pension to inflation, which would be lower than the current link to male total average weekly earnings.

Mr Hockey says too many people are relying on government payments and the issue needs to be addressed.

"Obviously we've got to have a sustainable welfare system and there is a serious question as to whether our current welfare system, which was designed in the 20th Century, is sustainable in the 21st Century when we have significant demographic challenges," he said.

Opposition spokesman Tony Burke says the Government is about to break an election-eve pledge not to change the age pension.

"The promise was - no changes. Full stop. No qualification. No changes to pensions," Mr Burke said.

"If we go through the budget and in the budget there are no announced change to pensions, then that promise may not have been broken, but that is not the way Joe Hockey is talking today."

Greens leader Christine Milne says it is unreasonable to expect people with physically demanding jobs to work until they are 70 before they are eligible for the age pension.

"Apart from asking people, especially those who've worked in a physically demanding jobs all their lives to keep working until they're 70 - if they can't they'll have to go onto New Start which won't in any shape or form be able to support them," she said.

National Seniors chief executive Michael O'Neill says a further rise in the pension eligibility age may be inevitable, but it will not make a difference if employers will not take on older workers.

"We think at the moment it's quite irrelevant as a debating point," he said.

"And quite simply, the failure of any government to satisfactorily deal with mature age employment means that all you're doing in shifting the pension eligibility age is shifting people from one form of welfare to another."

Mr O'Neill says older Australians would be left worse off if their pensions were directly linked to the inflation rate, or Consumer Price Index (CPI).